Modern aircraft are typically flown by a computerized autopilot (AP) The AP interfaces with Flight Control computers that are coupled both to actuators coupled to control surfaces and to engine computers such as a fully automated digital control (FADEC) computer. Together these cause the aircraft to follow a prescribed path and to maintain proper lift. A navigational computer or flight management system (FMS) receives pilot input regarding intended lateral path to a destination and either receives a vertical flight plan or develops the vertical flight plan based on pilot input, the present position and condition of the aircraft, and current flying conditions such as wind. The vertical and lateral flight paths are typically represented as a series of interconnected waypoints describing a path between points of departure and arrival. The FMS directs the AP to pilot the aircraft according to the flight plan.
In some instances, constraints are input to the AP based on instructions from ground based air traffic control (ATC) systems constraining the flight path of the aircraft. These constraints are typically an altitude ceiling above which the aircraft is not permitted to fly or an altitude floor above which an aircraft must fly. The constraints preempt control of the AP by the FMS. The FMS may nonetheless direct the AP to the extent a planned flight path does not conflict with AP constraints.
A surveillance system monitors hazards around the airplane and along a predicted flight path. Hazards include weather systems, turbulence, mountains, other aircraft, volcanic ash, and the like. The location of hazards is displayed to the operator of the aircraft (whether onboard or remote) by means of a screen or heads up display in the cockpit. Hazards may be displayed in a navigational, or plan, display illustrating the horizontal position of the aircraft and hazards. Hazards may also be displayed in a “vertical” display, showing the position of the aircraft and hazards in a vertical plane.
In the navigational display, it may not be immediately apparent that an aircraft's altitude carries it above or below a hazard such that the hazard does not require attention. Likewise, in the vertical display hazards are not apparent that are slightly to one side or the other horizontally from the aircraft's flight path. In some systems, the surveillance system visually distinguishes symbology representing hazards according to whether the hazards lie along a predicted flight path, or within a specific tolerance of a predicted flight path. Distinctive representation of hazards enables a pilot to focus attention on hazards likely to be encountered by the aircraft. For example, in FIG. 1, the aircraft 10 flying along the predicted flight path 12 is likely to encounter hazard 14a whereas hazard 14b does not lie on the predicted flight path. Accordingly, a navigational display 16 might appear as in FIG. 2 having hazard 14a represented in a solid color whereas hazard 14b is shown with hash marks. Distinctive representation may be accomplished by other markings, fill patterns, colors, and the like. In some systems, a surveillance system is programmed to issue audible, pictorial, and/or textual alerts when a hazard is found to lie along a predicted flight path. Accordingly, the surveillance system distinguishes between on- and off-path hazards when determining whether to issue an alert.
The AP, FMS, surveillance system, and various control panels are typically embodied as discrete autonomous units, interfacing with one another in precisely defined ways. The criticality of each of the components means that each must be carefully tested and certified by regulatory agencies before being approved for installation. Modification of the components requires similar testing and regulatory approval. Modification of the AP and associated control panels in particular is an extremely complicated and expensive process because its role in control of the aircraft is so vital.
In one system, the surveillance system receives the planned flight path determined by the FMS. The surveillance system may also be notified of any constraint that has been imposed, such as an altitude ceiling or floor, though in some systems no notice is given and imposition of the constraint is detected by other means. The surveillance system does not receive notice when the constraint ceases to be active. Accordingly, the surveillance system is unable to determine when the aircraft is no longer subject to the constraint and is therefore unable to determine whether the predicted flight path will follow the constrained flight path or the unconstrained planned flight path.
This problem arises in the scenario of FIGS. 3A and 3B illustrating a planned flight path 18 in the vertical view. An aircraft 10 may follow an actual path 20 passing through, or “sequencing,” a waypoint 22 forming part of the planned path 18 within an area in which a constraint 28, such as an altitude ceiling (FIG. 3A) or an altitude floor (FIG. 3B) is in effect. At point 30, the actual path 20 of the aircraft 10 transitions from following the planned flight path 18 to conform to the constraint 28. At point 32 the aircraft 10, the aircraft 10 begins to follow the planned path 18 and directs itself toward waypoint 34. In FIG. 3A, the aircraft 10 transitions to the planned path 18 because it lies below the constraint 28. In FIG. 3B, the aircraft 10 transitions because the constraint 28 is changed to an altitude lying below the planned path 18. At points 30 and 32 the surveillance system is not notified which path will be followed as the aircraft 10 moves forward. Accordingly, it is not apparent for which of the hazards 14a-14c to provide alerts.
Accordingly, it would be an advancement in the art to provide systems and methods for resolving which of the constrained flight path and unconstrained flight path will be followed by the aircraft. It would be a further advancement in the art to provide such systems that do not require modification of the AP or the FMS.